The present invention relates to a rotary actuator for an adjuster of a vehicle seat, in particular of a motor vehicle seat, with the rotary actuator having: a manually actuatable operating element; a transmission gearing on which the operating element acts when actuated; and an output element that is rotated at least intermittently by the transmission gearing and, during a rotation, drives the adjuster, with the transmission gearing changing during the actuation by the operating element from a higher transmission ratio to a lower transmission ratio.
In the case of a rotary actuator of the above-described type that is disclosed in DE 100 57 377 C1 (which is a member of the same patent family as US 2003/0116689) and has levers in rolling contact with one another, a gearing is provided which, when there is a rise in the driving torque, for example in response to an increased counterforce of the adjuster to be driven, provides a continuous reduction of the transmission ratio in order to avoid an overload. If the adjuster which the rotary actuator is to drive is provided with elements which adjust without any play (e.g., springs), then before the actual adjusting movement the path covered by the elements which adjust without any play has to be passed through counter to the force thereof. If a large actuating path for the operating element is not available, this efficiency of the rotary actuator that is initially and subjectively perceived to be low may be regarded by the user as being uncomfortable.